While both oscillator devices and phase-locked loop (PLL) circuits are used for frequency synthesis in generating output clock signals, internal oscillator circuits typically differ from PLL circuits in the stability or drift of the output frequency. For example, while PLL circuits are able to lock certain frequencies under the majority if not all conditions of temperature and power supply variations, internal oscillators generally suffer from frequency drift over the given temperature range. In addition to failing to produce the level of accuracy for PLL generated clock circuits, internal oscillator circuits typically have a limited frequency range.
Attempts to address the limitations of oscillator circuits typically include the use of external clocks and/or crystals, e.g., using an on-chip PLL circuit as a clock source. Such techniques come at a significant cost of silicon area, as well as requiring complex analog circuitry, such as the use of loop filters and highly accurate external clock sources, to make such a circuit operate properly.